As an analytical chemist, I'm always ensuring my glassware is thoroughly clean before I start an analysis. However, my supervisor always states that using ultrasonic bath to clean volumetric glassware damages its calibration, rendering it imprecise for analytical usage. Does that hold true, or is it okay to use an ultrasonic cleaner?

$\begingroup$Unless it fractured the glassware I don’t see the issue.$\endgroup$
– Jon CusterJun 21 at 19:26

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$\begingroup$I sometimes sonicate volumetrics to help dissolution for a short period. However, I am actually curious about the following test, which I vaguely recall (and therefore could be wrong). If we make up the volume exactly to mark, and then sonicate, what happens to meniscus? It goes down slightly below the mark temporarily. This could be from local heating of the glass. Glass and solutions do heat up during sonication.$\endgroup$
– M. FarooqJun 22 at 2:34

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$\begingroup$A temporary effect due to temperature is sure. But volumetric glassware is supposed to be used at about room T.$\endgroup$
– AlchimistaJun 22 at 10:39

2 Answers
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Both glass and plastic labware may be cleaned in an ultrasonic bath. However, direct contact with the sonic membranes must be avoided.

Nevertheless,

For gentle treatment of labware, clean immediately after use – at low temperatures, with brief soaking times, and at low alkalinity. Glass volumetric instruments should not be exposed to prolonged immersion times in alkaline media above 70 °C, as such treatment causes volume changes through glass corrosion, and destruction of graduations.

If your supervisor is unconvinced by Brand's guidance on this (as supplied by Loong in his answer), you could always test the effect of ultrasonic cleaning directly:

Take, say, six volumetric flasks, and weigh the amount of water each holds when filled to the line. Then subject three to several cycles of ultrasonic cleaning (the other three can be left to sit in the ultrasonic cleaning solution, but without turning the machine on), dry all six, and repeat the weighing measurement. Determine if the before-and-after difference for the ultrasonically cleaned flasks is significantly different from that seen in the control flasks.

While the control flasks do control for temperature differences between the before-and-after measurements, it would be cleaner if you could do the before-and-after measurements at the same temperature. That way the only difference you see should be random experimental error plus any systematic differences due to cleaning.

[Or more simply, if your boss is unconvinced by Brand's guidance, you could ask Brand if they could supply their test data on the effect of sonication.]

EDIT, BASED ON COMMENTS: If cumulative damage is the concern, then one could always employ an accelerated wear technique. In this case, one would increase the sonication time until it matched the total sonication time anticipated over the lifetime of a volumetric flask. E.g., if standard cleaning time is 20 minutes, and glassware is typically cleaned 600 times, then one could leave it in the sonicator continuously for 8 days (assuming the sonicator wouldn't be damaged by this). If you don't have a spare sonicator, you could do this over four successive weekends. Or perhaps one weekend would be sufficient to satisfy your manager.

Note that this accelerated wear technique is a standard method used in product testing -- e.g., if you have a part that over its, say, 10-year lifetime is expected to be flexed no more than 10,000 times, then you put it in a device that does those 10,000 flexes over a very short period of time (or does sufficient flexes on several parts to determine a mean time to failure).

$\begingroup$I suspect his adviser's objection is to repeated cleanings, not a single (or even short cycle) event. For the experiment to hold true, you'd need to perform potentially hundreds of cleanings.$\endgroup$
– ValorumJun 22 at 7:07

$\begingroup$@Valorum No. Put it in the ultrasonicator over the weekend and be done with it. Of course the result will be the same, glass does not yield to ultrasound. Repeating the same experiment a thousand times just in the hope it will one day give a different result is not good scientific practice.$\endgroup$
– KarlJun 22 at 8:26

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$\begingroup$@Karl - A beaker in the lab might get re-used thousands of times. Unless you can adequately model what happens after x thousand cleanings, your results will be worthless. Cleaning a table with a too-harsh cleaner once won't usually harm it in any measurable way. Cleaning it hundreds of times will result in the patina coming off.$\endgroup$
– ValorumJun 22 at 8:48

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$\begingroup$@Karl It's not "repeating the same experiment a thousand times." It's possible that one ultrasonic wash doesn't make a large enough difference to measure, but that, over the life of a flask, the damage will add up to something significant. How many washes would a weekend correspond to?If it's something like a lifetime of washing, fine; if it's not, then it's not enough.$\endgroup$
– David RicherbyJun 22 at 12:25

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$\begingroup$Can anyone propose a mechanism that could impair a flask's calibration with repeated sonication? Does the advisor think cavitation will erode the flask's interior?$\endgroup$
– jeffBJun 22 at 17:37